Qff Fire Science

Front 1

What is the range of flammability?

Back 1

In order to support combustion, fuel vapor and air need to be mixed in the correct ratio. The range of concentrations is the Flammability Range. If the mix of air to fuel is too high (LFL) or the mix of fuel to air too high (UFL) then combustion will not take place.

Front 2

How does oyxgen work within a fire?

Back 2

Atmosphere is a 21% oxygen. If oxygen content is raised the fire becomes more vigourous. If oxygen drops below 12% fire will stop.

Front 3

What are the five types of heat energy?

Back 3

- Mechanical (friction heat from filing a BA cylinder)

- Electrical (arcing, static)

- Mechanical (friction heat from filing a BA cylinder)- Electrical (arcing, static)- Solar (from the sun)- Nuclear (splitting atoms)- Chemical (most common form)

- Mechanical (friction heat from filing a BA cylinder)- Electrical (arcing, static)- Solar (from the sun)- Nuclear (splitting atoms)- Chemical (most common form)

- Mechanical (friction heat from filing a BA cylinder)- Electrical (arcing, static)- Solar (from the sun)- Nuclear (splitting atoms)- Chemical (most common form)

- Mechanical (friction heat from filing a BA cylinder)- Electrical (arcing, static)- Solar (from the sun)- Nuclear (splitting atoms)- Chemical (most common form)

- Solar (from the sun)

- Nuclear (splitting atoms)

- Chemical (most common form)

Front 4

Name the four ways fire is extinguished?

Back 4

- Smothering (removing oxygen, sealing a ships hold)

- Starving (removing fuel)

- Cooling (removing heat)

- Interrupting chemical chain reaction (dry powder)

Front 5

Explain what is spontaneous heating and give two examples.

Back 5

Occurs when two materials increase in temperature due to a chemical recation with no external heat source.

Mixing paint and resin, oil soaked rags rolled into a ball

Front 6

Describe the process of pyrolysis.

Back 6

The decomposition or transformation of a solid into another form, caused by heat resulting in the production of ignition vapours or gases.

Front 7

Explain in detail how heat contributes to the combustion process.

Back 7

- Heat causes pyrolysis/decomposition resulting in the production of ignition vapours or gases

- Heat provides the energy necessary for ignition

- Heat causes the continious production and ignition of fuel vapours or gases so that the combustion reaction can continue

Front 8

Heat transfer, describe conduction, convection and radiation.

Back 8

Conduction. Heat will travel from areas of high temperature to areas of a lower temperature. Substances that are good thermal conductors will allow heat to travel away from the fire.

Convection. The transfer of heat through liquid or gas. In a fire convection currents carry hot gases upward.

he transfer of heat through liquid or gas. In a fire convection currents carry hot gases upward.

Radiation. Transferring heat energy out from the fire and warming nearby objects.

Front 9

What is fire point?

Back 9

Fire point is the lowest temperature at which sufficient vapour is given off to enable combustion if ignited, and will then continue to burn once ignition source has been removed.

Front 10

What is flash point?

Back 10

Flash point is the lowest temerature at which vapour emitted by a liquid will flash momentarily if ignited but not continue to burn. It burns out or self extinguishes when it has consumed all the vapour.

Front 11

What is spontaneous ignition temperature?

Back 11

The lowest temperature at which an substance will ingite with no external ignition source.

Front 12

Explain the term flashover in relation to a fire in a single room.

Back 12

Occurs when all the fuel items within the compartment ignite, virtually at the same time. Accompanied by extreme heat and large quantities of smoke.

Front 13

State three signs that flashover is about to occur.

Back 13

- Rapid rise in temperature in the compartment

- Tounges of fire in smoke layer

- Smoke rapidly backing down to floor

- All combustible surfaces giving off fumes or vapours

Front 14

State two actions that may reduce the risk of flashover.

Back 14

- Cooling the overpressure zone

- Venting the compartment

Front 15

What are some safety precautions when it comes to flashover?

Back 15

- Be aware of possible flashover, watch for warning signs

- Wear correct PPE

- Have an additional charged delivery covering the entrance

- Ensure escape routes are protected

- Check outsides of doors for heat before entering

- Stay low

- Controlled bursts of water into overpressure zone

- Ventilate only when officer tells you to

Front 16

Compare flashover to backdraft.

Back 16

Flashover happens often, causes rapid fire development, trigged by heat build up, must be a venilated fire.

Backdraft is rare, a violent recation, trigged by a sudden in rush of freshair, may occur in growth or decay phase.

Front 17

What is backdraft?

Back 17

A sudden erruption of fire in an underventilated compartment due to the introduction of fresh air.

Front 18

What are the warning signs of backdraft?

Back 18

- Smoke puffing from windows, doors and around eaves

- Black smoke and soot stained windows

- Excessive heat when feeling back of door

- Windows rattling and appearing oily

- Sudden in rush of air when opening is made

- Little or no visible sign of fire within compartment

- Muffled sounds within the compartment

Front 19

What are the safety precuations for backdraft?

Back 19

- Ensure proper PPE is worn

- Keep doors closed, cover with charged branch and stay low

- Keep out of room if possible

- Cool as much of the compartment as possible; direct water spray upwards

Front 20

How do you minimise the risk of backdraft?

Back 20

- Prevent oxygen from entering and wait until the compartment cools

- Cool the environment

- Remove flammable vapours

Front 21

Whare are the phases of fire development

Back 21

- Incipient

- Growth

- Fully developed

- Decay

Front 22

Describe the Incipient phase of fire development.

Back 22

- The ingredients of combustion come together and ignition occurs

- Smoke detectors can sound as smoke is often generated before ignition

- Duration can be a few milliseconds or several days

- Fire can go out if the fire triangle is split

Front 23

Describe the Growth phase of fire development

Back 23

- Begins with self-sustaining combustion, which continues to burn once ignition source is removed.

- Growth rate depends on ventilation, fuel properties and compartment size

Front 24

Describe the Fully Developed phase of fire development .

Back 24

- Most damage occurs in this phase, as all fuel is consumed.

- Fire continues to burn with high heat release and high temperatures.

- Heat is transferred by convection, conduction, radiation and direct burning.

- Duration depends on the amount of fuel and ventilation available.

Front 25

Describe the Decay phase of fire development.

Back 25

- Starts once 80% of fuel has been consumed.

- Rate of heat declines until all the fuel has been consumed and fire goes out.

- Duration depends on the characteristics of the fuel.

Front 26

Briefly explain how water extinguishes a fire.

Back 26

Water absorbs large amounts of heat by its change of state from liquid to steam.

Front 27

Water has a high latent heat of vaporization. Explain the significance of this in relation to using water to extinguish fires.

Back 27

Waters lateby heat of vaporization is used in firefighting when heat energy is absorbed from the fire by water, as it changes state from liquid to steam. To act as a cooling agent, you need to spray the water which provides the best surface area for efficient conversion to steam.

Front 28

Explain the effect steam has on a fire.

Back 28

A lot of the heat energy is absorbed into converting water to steam. For maximum cooling effect, spray pattern needs to be on fog/spray to convert a greater amount of water to steam. Water converted to steam at 100C will expand to 1,700 times its original volume.

Front 29

Why is water a good extinguisher?

Back 29

- It is reasonably cheap, readily available and efficient.

- Most effective due to its cooling properties.

- Water absorbs a lot of heat energy from fire.

- Most heat is absorbed during waters change of state from water to steam.

Front 30

When should you not use water at fires?

Back 30

- For burning liquids that are immiscible with water but less dense than water.

- Calcium carbide

- Sodium peroxide

- Quicklime

- Concentrated sulphuric acid

Front 31

What does a solid surface-to-mass ratio mean?

Back 31

- The greater the surface-area-to-mass-ratio, the quicker the fuel will reach ignition temperature

- The greater the surface area, the more radiant heat the fuel will receive.

- The smaller the mass, the less heat energy is needed to raise it to ignition temperature.

Front 32

Fire is a chemical process which has three main components. Name these three components and give examples of how these can be present at an MVA scene.

Back 32

Fuel - petrol and synthetic fibres in seating

Heat - hot engine or battery arcing

Oxygen - breathable air or if vehicle has compressed air cylinders or oxygen bottles on board.

Front 33

Describe the process that occurs when a solid burns.

Back 33

The applied heat is absorbed into the mass and dissipates to some degree. However, when the amount of applied heat exceeds the ability of the mass to dissipate the heat, chemical breakdown occurs and the self-sustaining burning reaction results and continues.

Front 34

Give three examples of fires being extinguished by smothering.

Back 34

- Snuffing a candle

- Putting a lid on a burning pot

- Applying a foam blanket

Front 35

What is flashback?

Back 35

When a fuel is still emitting flammable vapours after it has been smothered, it will easily reignite with any resupply of oxygen.

Front 36

What is auto-ignition temperature?

Back 36

The lowest temperature at a substance will ignite without a pilot flame.

Front 37

What is flashpoint?

Back 37

The lowest temperature at which sufficient vapour is emitted by a liquid to flash momentarily if ignited but not continue to burn.

Front 38

Explain in detail how heat contributes to the combustion process.

Back 38

Heat causes pyrolysis, resulting in the production of ignition vapors or gases. It also provides the energy necessary for ignition and causes continuous production, and ignition of fuel vapours or gases so the combustion reaction can continue.

Front 39

How is heat lost in combustion?

Back 39

- Heating up the unburnt fuel

- Chemically break down the fuel

- Radiation into the environment

- Convection in the rising smoke

Front 40

Briefly describe the combustion process.

Back 40

A chemical chain reaction between a fuel and an oxidant, resulting in the production of heat which makes the combustion self-sustaining.

Front 41

What is the ideal mixture?

Back 41

The ratio of oxygen to vapours at which a substance will burn most intensely with the hottest flame.

Front 42

What is the Lower Flammability Limit?

Back 42

The lowest ratio of fuel to oxygen that will support combustion. Fuel lean.

Front 43

What is the Upper Flammability Limit?

Back 43

The highest fuel to air ratio that will support combustion. Fuel rich.

Front 44

What are the three constitutes of smoke?

Back 44

- hot vapour and gases

- unburnt decomposition

- air heated by fire

Front 45

What is Heat Release Rate?

Back 45

The heat energy released over time in a fire. Describes how big the fire is.

Front 46

What is the Over Pressure Zone?

Back 46

An upper layer of hot buoyant smoke and fire gases.

Front 47

What is the Under Pressure Zone?

Back 47

A lower layer containing cooler, denser air.